Results & discussion points

Cautionary notes

The performance of agronomic treatments and varieties varies between locations and years. New agronomy or varieties should be tested on a small scale to ensure they are suitable for different locations and farming practices, as results from our experiments may not be repeated at different locations or in different years. Some of the varieties are not commonly grown in the Northern Region so it is important to ensure they can be marketed before choosing to sow them. Finally, because diseases were controlled in these experiments, some varieties discussed in this paper could perform differently in an environment/year with high disease pressure if fungicides were not used.

Season conditions in 2014 & 2015

The 2014 season was generally cooler and had higher yield potential than 2015 (in which most sites experienced a hot finish). Frost was not considered to have had an effect on yield in any of the experiments. Lodging was easily induced in 2014 at all locations, but in 2015 substantial lodging was only observed at Gatton.

Effect of sowing date on lodging and yield

Earlier sowing is known to give higher wheat yields in dryland situations, if frost can be avoided. However in irrigated conditions there is a risk that when lodging risk is high, earlier sowing may increase lodging and decrease yield. This was observed at two sites in 2014; Narrabri and ‘Spring Ridge - Delayed N’ (Figure 1). However, in the other two 2014 experiments (Emerald, ‘Spring Ridge - Sowing N’)  the opposite effect was observed, as storms caused worse lodging in the greener, later sown plots, leading to lower yields.

In 2015, a large yield advantage was observed in the early sown treatments at all sites, no doubt due to the hot dry finish and absence of any significant lodging (Figure 1).

Figure 1. Effect of sowing date on yield and lodging (calculated as the mean of all varieties) for experimental sites in 2014 and 2015

The effect of N-application timing on yield and lodging for different varieties and locations

Previous experiments at Gatton have shown that wheat can recover extremely rapidly from N stress in a subtropical environment. We have begun detailed experiments to examine the best strategy for N application and whether it is the same for all varieties in different locations. This was only the first year of these experiments so the results should be treated with caution.

At Gatton in 2015, the results showed that for the quick maturing varieties Suntop and Kennedy, the best-practice N application strategy (‘200 by GS31’) yielded more and lodged less than the sowing N strategy (Figure 2). Later application of N made only a small difference to grain yield and remarkably, the ‘very late’ strategy yielded similarly to the sowing N strategy despite having been severely N stressed at GS39. These results are typical of previous canopy management experiments we have conducted in sub-tropical locations.

Figure 2. Effect of N strategy on yield and lodging of the quick varieties Suntop and Kennedy at Gatton, 2015

However, the longer season varieties at Gatton showed a different response to N timing (Figure 3). Cobra and Trojan had higher yields associated with the ‘200 by GS31’ treatment compared to the Sowing N treatment, but did not have a lodging reduction associated with the yield increase. Mitch and Lancer showed different trends, with Lancer showing a slight yield increase as N application was delayed further, and Mitch achieving the best yields when N was applied at sowing.

Due to changes in variety flowering response between environments, the varieties were allocated differently into the long season and quick maturing groups at Spring Ridge. It should also be noted that the results at Spring Ridge were influenced by the absence of any substantial lodging (hence no lodging graphs are shown). The longer season varieties (Figure 4) and most of the quicker varieties (Figure 5) at Spring Ridge generally yielded the best when N was applied at sowing. The exception was Cobra which yielded better in the ‘200 by GS31’ N treatment. The same trends may not have been observed if severe lodging had been experienced.

Figure 3. Effect of N strategy on yield and lodging of long season varieties at Gatton, 2015

Figure 4. Effect of N strategy on yield of long season varieties at Spring Ridge, 2015

Figure 5. Effect of N strategy on yield of quick varieties at Spring Ridge, 2015

Summary & conclusions

The results of the experimentation in 2014 and 2015 have challenged some of the established theory around avoiding lodging. Later sowing has been previously observed to reduce lodging – however we saw in the 2014 experiments that lodging was sometimes worse in later sown plots, because storm damage was greater in green crops than mature/dry crops.

Additionally, while ‘in-crop’ N application continues to reduce lodging risk for quick varieties in warm environments, we are not always observing the same trend in longer season varieties or alternative environments. While further experimentation is needed to examine more site x year combinations, it could be possible that newer, more lodging resistant varieties don’t respond to ‘in-crop’ N application as consistently as the older varieties we began experimenting with in 2009.

Acknowledgements

The research undertaken as part of this project is made possible by the significant contributions of growers through both trial cooperation and the support of the GRDC, and the authors would like to thank them for their continued support. We also thank farm and technical staff at the DAFQ Emerald Research Farm, CSIRO Toowoomba, the CSIRO Gatton Farm, and the University of Sydney’s Plant Breeding Institute (Narrabri) for their assistance in managing these experiments, along with Angus Murchison of Spring Ridge for hosting some of the experiments.

Further reading (available from the GRDC website)

Fact Sheet (Northern Region): ‘Reducing lodging risk in irrigated wheat’

GRDC Goondiwindi Update Paper (2012) by Peake et al. “Agronomy for high yielding cereal environments: varieties, agronomic strategies and case studies”

GRDC Goondiwindi Update Paper (2014) by Peake et al. “Beyond 8 t/ha: varieties and agronomy for maximising irrigated wheat yields in the northern region”

GRDC Goondiwindi Update Paper (2015) by Peake et al. “Irrigated wheat agronomy x variety trials: 2014 Trial Update”

Contact details

Dr Allan Peake
CSIRO Agriculture, 203 Tor St, Toowoomba.
Phone: (07) 4688 1137
Email: allan.peake@csiro.au